1. Field of the Invention
The present invention relates to a high-sensitivity semiconductor light detecting element that is less dependent on temperature and requires no film thickness control at the atomic layer level or the like.
2. Background Art
In order to make bandwidth in a semiconductor light detecting element wider, it is required to reduce the film thickness of the light absorbing layer. However, if the film thickness of the light absorbing layer is reduced (for example, InGaAs: film thickness of 0.5 μm to 2 μm), sufficient light detecting sensitivity cannot be obtained. In addition, at low temperatures, since the band gap of the light absorbing layer is larger, the sensitivity is further lowered.
It has been reported that in the semiconductor mixed crystal of the III-V group including Bi, the temperature change in the band gap becomes small together with the amount of Bi, and especially the band gap (0.6 to 1.5 eV) of InGaAsBi becomes constant to the temperature change (for example, refer to Japanese Patent Laid-Open No. 9-8405). It has also been reported that temperature characteristics of a semiconductor laser by using InGaAsBi in a layer other than the active layer is improved (for example, refer to Japanese Patent Laid-Open No. 2000-223787 and Japanese Patent Laid-Open No. 2004-221413).
A semiconductor optical element has further been reported that consists of a short period superlattice, wherein the thin film of an active layer using two kinds of III-V group semiconductors or its mixed crystal as the constitution unit, and the thin film having the largest lattice constant contains Bi (For example, refer to Japanese Patent Laid-Open No. 11-68238). For example, a short period superlattice of (InAsBi)m(GaAs)n, wherein Bi is contained in InAs having the larger lattice constant in InAs and GaAs is used as the active layer.